Dynamics of subsurface soil erosion in a semiarid region: A time-series study of sinkhole area and morphology

Subsurface soil erosion causes irreversible damage to agricultural fields by generating elongated pipes and elliptical sinkholes that can further develop into rills and gullies. However, despite their severe consequences, there is still limited available quantitative information on spatiotemporal dynamics of soil pipes and sinkholes, especially in semiarid regions; evidence of subsurface erosion rates is based on a small number of time points during a sampling period that is usually limited to a few successive years. Here, temporal changes in sinkhole area, and their level of circularity and orientation were quantified over a decade (2010–2020), in loess-derived soils in the semiarid Negev desert, Israel. Data were measured using high-resolution aerial photographs (1 pixel = 15 cm length), and were related to high-temporal-resolution rainfall data. The results revealed that: (1) soil pipe collapse is related to early winter rainfall events more than to mid or end-of-winter events, possibly due to the development of annual herbaceous vegetation that shields the soil and increases its resistance to erosion; (2) sinkhole and soil pipe morphological development and orientation are related to the orientation of stream banks and the tension cracks developed along those banks; and (3) changes in sinkhole area are related to catastrophic rainfall events and not to gradually accumulated annual rainfall.